1. Field of the Invention
The present invention relates to the field of current measurement technology. It concerns an optical current transformer which makes use of the Faraday effect for the purpose of measuring a current, comprising
(a) a sensor element having an optical entrance for coupling in light and at least one optical exit for coupling out the light; PA1 (b) within the sensor element, an annular waveguide which encloses the current to be measured and is optically connected to the optical entrance and the at least one optical exit; and PA1 (c) means for measuring the magneto-optical rotation of the plane of polarization of the light in the waveguide. PA1 (d) the sensor element comprises a flat substrate with a continuous opening, situated at the center, for the current to be measured; PA1 (e) the waveguide is designed as an integrated-optics single-mode waveguide embedded in the substrate; and PA1 (f) the waveguide encloses the opening in at least one winding. PA1 (a) the substrate consists of a glass; and PA1 (b) the waveguide has been generated by exchange of ions in the glass.
Such a current transformer is known, for example, from DE-A1-3,116,149.
2. Discussion of Background
Optical current transformers which make use of the Faraday effect in a suitable material, especially a glass fiber, for the purpose of measuring the current, are known from a multiplicity of publications. By way of representative examples, reference is made in this connection to the following publications:
"Magnetooptical current transformer. 1: Principles", A. Papp et al., Appl. Optics 19 (1980), pp. 3729-3734; PA0 "Magnetooptical current transformer. 2: Components", H. Aulich et al., Appl. Optics 19 (1980), pp. 3735-3740; PA0 "Magnetooptical current transformer. 3: Measurement", H. Harms et al., Appl. Optics 19 (1980), pp. 3741-3745; and PA0 "Magneto-optical fiber sensors for electrical industry: analysis of performances", S. Donati et al., IEE Proc. 135 (1988), pp. 372-382.
In this connection, there are in the prior art various current transformer concepts which differ principally in the nature of the design of the sensor element or sensor head. In many cases, the sensor element consists of a glass fiber wound up in the manner of a coil (see the abovementioned publications). In other cases, the sensor is designed as a compact glass block which encloses the current path and in the interior diverts the light by means of mirror-coated corners around the current path (in this connection, see: "A new generation of current sensing", MOCT Technical Documentation Summary, Westinghouse ABB Power T+D Company, Electric Metering Systems, Raleigh, April 1989).
Various methods are employed for the evaluation of the measurement signal: one of these is the one-polarizer method, in which a single polarizer is disposed at the exit of the sensor for the analysis of the polarization (in this connection, see FIG. 1 of DE-A1-3,116,149). On the other hand, use is however also made of the polarimetric detection method, in which the polarization components in two mutually orthogonal directions are determined in a polarimetric detection unit (in this connection, see FIG. 3 of the above cited article by S. Donati et al.).
The earlier current sensors have the disadvantage either that they react sensitively (as in the case of wound glass fibers) to external disturbances of the waveguide, such as for example vibrations, change of temperature, mechanical pressure on the fiber, bending of the fiber, or that they are onerous and costly in production (as in the case of the mirror-coated glass block).